1. Technical Field of the Invention
The embodiments of the invention relate to wireless communications and, more particularly, to power conservation in a wireless mobile device.
2. Description of Related Art
Various wireless communication systems are known today to provide communication links between devices, whether directly or through a network. Such communication systems range from national and/or international cellular telephone systems, the Internet, point-to-point in-home systems, as well as other systems. Communication systems typically operate in accordance with one or more communication standards or protocols. For instance, wireless communication systems may operate using protocols, such as IEEE 802.11, Bluetooth™, advanced mobile phone services (AMPS), digital AMPS, global system for mobile communications (GSM), code division multiple access (CDMA), local multi-point distribution systems (LMDS), multi-channel-multi-point distribution systems (MMDS), as well as others.
Presently, in the mobile (e.g. cellular) telephone category, the trend is a transition from 3G (3rd Generation) to 4G (4th Generation). In one area of application, Long Term Evolution (LTE) is marketed as 4G LTE to provide high speed wireless data transfer to mobile phones and other mobile devices (e.g handheld devices, tablet computers, etc.). Typically, a transmitting node (such as a cellular tower) provides limited coverage within a given radius or area. The transmitting node is referred to as NodeB or eNodeB, where eNodeB stands for Evolved NodeB or E-UTRA (Universal Terrestrial Radio Access) NodeB.
For each wireless communication device, such as devices that utilize 3G and 4G communications, to participate in wireless communications, it generally includes a built-in radio transceiver (e.g., receiver and transmitter) or is coupled to an associated radio transceiver (e.g., a station for in-home and/or in-building wireless communication networks, modem, etc.). Typically, the transceiver includes a baseband processing stage and a radio frequency (RF) stage. The baseband processing provides the conversion from data to baseband signals for transmitting and baseband signals to data for receiving, in accordance with a particular wireless communication protocol. The baseband processing stage is coupled to a RF stage (transmitter section and receiver section) that provides the conversion between the baseband signals and RF signals. The RF stage may be a direct conversion transceiver that converts directly between baseband and RF or may include one or more intermediate frequency stage(s).
For handheld devices, where most or all of the components are resident in the device, the handheld device typically also includes an application processor or processors to execute various applications for the device. Although a given NodeB may communicate with multiple user devices (referred to as User Equipment or UE) within its area of transmission, generally communication links (or channels) between the NodeB and the UEs carry different signals. With separate unicast transmissions to each UE, the transmission protocols typically use an acknowledge (ACK) signal to indicate a reception of a transmission at the UE and/or a non-acknowledge (NACK) signal to indicate a non-reception or incomplete reception at the UE. In this manner, the NodeB can either transmit the next message, when the previous message is received, or retransmit the original message again, when the full message is not received at the UE.
Multimedia Broadcast Multicast Service (MBMS) is a different kind of transmission in which a broadcast from a given NodeB is communicated to multiple UEs within the transmission area. In this way, multimedia broadcasts, such as television shows, movies, concerts and other multimedia, may be simultaneously broadcast to a plurality of UEs in the area. However, unlike unicast transmissions, MBMS does not use ACK/NACK signaling to indicate reception or failure of reception of a message. This is necessitated by the desire not to overburden NodeB by the approximately simultaneous transmission of ACK/NACK signals from multiple UEs.
Instead, MBMS transmissions rely on transmitting the multimedia signal that utilize Forward Error Correction (FEC). A number of FEC schemes may be used. For example, Reed-Solomon code may be used. There is a theoretical optimal code that always decodes with k receive symbols out of N generated symbols. If N can be any number, this would be considered a fountain code. However, if N is fixed, the ideal code may be realized using a Reed-Solomon code, but it is computationally intensive. Otherwise, a non-optimal fountain code, with some small probability of failure with only k symbols, may be used. The close to optimal codes may not be optimal, but require lower computational complexity. LTE, for example, uses a fountain code that is close to optimal.
Accordingly, for MBMS transmissions, a given NodeB typically transmits K number of source symbols along with E number of repair symbols for encoding with the FEC. A selected number of repair symbols are sent to ensure that most or all of the UEs in the area are able to recover the broadcast using FEC. The unfortunate aspect of this technique is that some UEs are able to recover the broadcast with minimal number of repair symbols, while other UEs require a substantial number of repair symbols. Because all of the UEs receiving the broadcast stay active throughout the complete sequence of source and repair symbols, the UEs consume power to process all of the symbols, even when some of those repair symbols are not needed for recovering the source data.
Accordingly, there is a need to provide a technique of conserving power by shutting down the processing of repair symbols once an adequate number of repair symbols have been decoded to recover the source multimedia data.